At a work site of a production facility, for example, a pair of pipes is arranged such that their flanges are butted together with a gasket interposed in between, and the pipes in such a state are connected together by tightening a plurality of bolts of the flanges. Usually, such work of fastening the flanges together by bolts is manually performed by a worker.
In order to keep stable connection between the pipes and prevent leakage from the pipes (flange leakage) for a long term, it is important to properly tighten the bolts at the flanges of the pair of pipes and check the tightened state of each bolt at the time of, for example, maintenance and periodic turnaround. In this respect, for example, Patent Literatures 1 and 2 disclose configurations in which a gasket disposed between a pair of flanges is provided with electrodes and pressure sensors, and thereby the tightened state of each of bolts fastening the flanges is monitored.